1. Field of the Invention
The present invention relates to a brushless synchronous motor that changes current supply to a plurality of phase-coils based on the rotation angle of a rotor detected by an encoder.
2. Description of the Related Art
In a brushless synchronous motor having a plurality of phase coils, current supply is shifted from one to another of the phase coils according to the rotation angle. The rotation angle is detected by an encoder that is composed of a rotor on which a permanent magnet is mounted and a magnetic sensor element such as a hall IC element fixed on a circuit board. Such a magnetic sensor element detects magnetic flux provided by the permanent magnet, as disclosed in JP-A-2004-48908 or U.S. 2004/0007935 A1, a counterpart of the former.
In order to make the brushless motor synchronous, the position of rotor teeth relative to stator teeth has to be detected at a high accuracy. Therefore, it is necessary to locate the magnetic sensor accurately relative to the stator. This is rather difficult because there are a lot of parts between the magnetic sensor and the stator, such as a circuit board, terminals and bobbins, which usually give dimensional variations. For instance, the magnetic sensor is fixed to the circuit board, and the stator core is fixed to a stator housing via the terminals and the bobbins.
The stator terminals are insert-molded into the stator housing. Those of the stator terminals on the side of the stator bobbins are located annularly along the stator winding to extend in the axial direction of the stator housing. Therefore, great care is necessary when the bobbins are assembled into the stator housing without damage of the stator terminals.